1. Field of Invention
The present invention relates to a lubrication system installed in a multi-cylinder engine (internal combustion engine) for vehicles such as automobiles, for example. In particular, the present invention provides a so-called dry-sump lubrication system.
2. Description of Related Art
In general, a dry-sump lubrication system takes out oil and blow-by gas from the lower portion of the engine with a scavenge pump and temporarily stores the oil in an oil tank located separately from the crank chamber. The lubrication system supplies the oil in the oil tank with a feed pump to portions of the engine to be lubricated, where lubrication or temperature adjustment (cooling or heating) is required. Thus, friction at sliding and rolling portions is reduced, and temperature adjustment (cooling or heating) is performed in various portions of the engine.
According to the dry-sump lubrication system, the oil storage space, which is provided in the lower portion of the engine in the related art, can be made significantly small, or even omitted, which allows downsizing of the engine and lowering the center of gravity of the engine. Besides, oil can be stored stably in the oil tank, and therefore can be prevented from leaning to one side or foaming in the crank chamber. Oil can thus be stably supplied to the portions of the engine to be lubricated.
In the lubrication systems disclosed in Japanese Patent Application Publication No. 2000-227016 (JP-A-2000-227016) and Japanese Patent Application Publication No. 2004-156451 (JP-A-2004-156451), oil in the oil pan provided at the lower portion of the engine is taken out by a single oil pump. In JP-A-2000-227016 and JP-A-2004-156451, the arrangement of components such as the oil collection passage and the scavenge pump is not described in detail.
Moreover, Japanese Patent Application Publication No. 2007-2806 (JP-A-2007-2806) discloses a multi-cylinder engine equipped with a lubrication system, in which oil at the bottoms of separately partitioned crank chambers is permitted to drop from oil discharge ports that are opened in the bottoms of the crank chambers into a single oil collection chamber located under the crank chambers. The oil in the oil collection chamber is taken out by a single scavenge pump.
This related art is disadvantageous in lowering the center of gravity of the engine since the oil collection chamber is located under the crank chambers of the engine. In addition, since the engine is a multi-cylinder engine, in which a plurality of pistons move up and down at different timings each other, the phases of pressure variations that occur in the crank chambers are also different. This increases the pressure difference between the crank chambers. Therefore, it is concerned that the oil in the oil collection chamber may flow back into crank chambers at a negative pressure, and that the scavenge pump may not be able to smoothly collect the oil.
Although the lubrication systems in accordance with the above related arts use a single scavenge pump and are therefore advantageous in terms of cost, weight, and installation space, the oil collection efficiency may be low as discussed above.
Japanese Patent No. 3052002 discloses an arrangement for a single-cylinder engine equipped with a dry-sump lubrication system, in which an oil path extending from a scavenge pump to an oil tank is formed in the mating surfaces of a crankcase and a crankcase cover of the engine. This lubrication system, however, relates to a single-cylinder engine and does not relate to a multi-cylinder engine. Japanese Patent No. 3052002 discloses that the lubrication system is also applicable to multi-cylinder engines, but does not at all disclose how the lubrication system can be applied to the multi-cylinder engines.